Influenza is a highly contagious acute respiratory disease which is of major concern to public health. Severe influenza can trigger acute respiratory distress syndrome (ARDS), for which treatment options are limited. The objective of this proposal is to characterize a novel host determinant that can serve as a target for new drugs to prevent or attenuate development of ARDS in influenza. Alveolar type II (ATII) cells are the site of influenza A virus replication in the distal lung and essential to normal lung function. ATII cells synthesize phospholipids, which are essential for both ATII cell mitochondrial respiration and surfactant function. However, effects of in vivo infection on the ATII cell surfactant lipidome, and their consequences for mitochondrial respiration have not been investigated. Preliminary studies indicate that influenza infection of C57BL/6 mice results in impaired production of CDP-choline and CDP-ethanolamine, which are liponucleotide precursors for de novo synthesis of the major phospholipids (phosphatidylcholine, phosphatidylglycerol, and phosphatidyl- ethanolamine). Development of ARDS is also associated with abnormalities in carbohydrate and fatty acid metabolism, as well as mitochondrial dysfunction and dysmorphology. However, inhibition of CDP-choline synthesis is not a result of reduced expression of CCT-?, which catalyzes its production. Influenza-induced ARDS, but not viral replication, is attenuated by post-infection treatment with exogenous liponucleotides. The hypothesis of this proposal is that influenza A virus inhibits ATII cell liponucleotide synthesis, which results in impaired phospholipid generation, reduced surfactant function, altered mitochondrial respiration, and progression to ARDS. This hypothesis will be tested in three complementary Specific Aims, which will show that: 1) Treatment with exogenous lipoNTs attenuates ARDS and improves surfactant function in influenza-infected mice; 2) Disruption of ATII cell Plipid synthesis results in mitochondrial dysfunction, altered energy metabolism, and ATII cell apoptosis; and 3) Impaired ATII cell lipoNT synthesis results from phosphorylation of liponucleotide synthesis enzymes by MAP kinases. Studies will use clinically-relevant measures of ARDS severity and state- of-the-art assays to determine effects of influenza infection on mitochondrial respiration. The goal will be to show a causal relationship between impaired ATII cell phospholipid synthesis, mitochondrial dysfunction, and development of ARDS in influenza-infected mice. Completion of these Aims will generate fundamental new information regarding the role of altered ATII cell lipid metabolism in the pathogenesis of influenza-induced ARDS. It will also provide proof-of-concept that parenteral liponucleotide supplementation can delay onset or reduce severity of influenza-induced ARDS, which will transform our current approach to its treatment.